The field of the invention is self-extinguishing, fine particulate, expandable styrene polymers for the preparation of molded articles. The present invention is particularly concerned with expandable, particulate molding compositions of styrene polymers containing organic halogen compounds and a synergist as flame proofing agents.
The state of the art of expandable polystyrene may be ascertained by reference to the Kirk-Othmer, "encyclopedia of Chemical Technology," 2nd Edition, Vol. 9 (1966) under the section entitled "Foamed Plastics," pages 847-884, particularly pages 852, 853 and 855 where polystyrene is disclosed, and Vol. 19 (1969) under the section entitled "Styrene Plastics," pages 85-134, particularly pages 116-120, where polystyrene foams are disclosed and pages 120, 121 where prior art self-extinguishing polystyrene foams are disclosed in U.S. Pat. Nos. 3,058,926; 3,058,927; 3,274,133; 3,389,097; 3,457,204; 3,789,028; 3,897,373 and 3,972,843; the disclosures of which are incorporated herein.
The disclosure of assignee's U.S. Pat. No. 2,954,412 is incorporated herein to show the preparation of dibenzylbenzene starting materials useful in the present invention.
U.S. Pat. No. 3,972,843 discloses methods, useful in the present invention, for producing particulate molding compositions for the production of foamed articles by polymerizing styrene in aqueous suspension.
It is known to use halogenated materials, especially organic bromine compounds, as flame proofing substances for self-extinguishing thermoplastic polmers. To achieve a sufficient effect, relatively large amounts of the halogenated compounds must be added. This adversely affects the processing properties especially as regards expandable polymers.
Further, it is known that the amount of the halogenated compound needed to keep the effect constant can be decreased by adding synergistic substances. The following particular synergists are known: organic peroxide compounds such as disclosed in U.S. Pat. Nos. 3,058,926 and 3,058,927 and diazo compounds such as disclosed in U.S. Pat. No. 3,897,373. Both organic peroxides and diazo compounds suffer from the drawback that they, as well as their dissociation products are highly toxic in the high concentrations required and that on occasion they decompose explosively.
The use of polymers and oligomers of p-diisopropylbenzene as synergists for brominated fireproofing agents as disclosed in U.S. Pat. No. 3,457,204, French Pat. No. 14 57 547 and Belgian Pat. No. 704,666 suffers from the drawback that these polymers and oligomers are insoluble in styrene and furthermore, they are present in the solid aggregate state, whereby it is difficult to introduce them into expandable styrene polymers. Furthermore, as regards a good effect, concentrations exceeding 1% by weight are required.
The use of the N-nitroso compounds as disclosed in U.S. Pat. No. 3,274,133, of triphenylphosphine oxide as disclosed in French Pat. No. 14 10 556 or of tetraphenylhydrazine, as disclosed in French Pat. No. 12 45 593 is prohibited in practice because these materials or their decomposition products are toxic.